The invention relates to a process for the stopping and restarting of an arrangement for open-end friction spinning having two rollers that are drivable in the same rotational direction and form a wedge-shaped gap serving as the yarn forming zone.
In the case of a known process (DE-OS No. 34 16 886), it is provided that the yarn guard reduces or completely interrupts the suction effect of the suction device in the case of a yarn breakage. The reducing as well as the complete interruption of the suction effect of the suction device have certain problems. If the suction effect is only reduced and not interrupted, the subsequent returning of a yarn end into the area of the wedge-shaped gap causes difficulties for a restarting procedure, particularly if this return of the yarn end is to be carried out by pneumatic means. If, on the other hand, it is provided that the suction effect is completely switched off in the case of a yarn breakage, there is the danger that the fiber residues or the like that are still located in the wedge-shaped gap are twisted together into a yarn worm. Fibers of this yarn worm may be taken out of the wedge-shaped gap by the roller rotating out of the wedge-shaped gap, and brought to or thrown off at a point that is hardly accessible for cleaning.
An object of the invention is to provide a process in which, on the one hand, the return of a yarn end for the restarting is not impaired, while, on the other hand, fiber residues and the like that are still in the wedge-shaped gap are not brought out of the area of the wedge-shaped gap in an uncontrolled way.
This object is achieved by the fact that in the case of a yarn breakage, the suction device is switched in two steps in such a way that until the time of a cleaning of the wedge-shaped gap, the effect of the suction device is reduced. The suction device is then interrupted during the return of the yarn end.
The reduced suction effect is dimensioned in such a way that, on the one hand, it does not pull the fiber residues that are present in the form of a yarn worm into the wedge-shaped gap and jammed in. On the other hand, the suction effect is large enough that the yarn worm is held in the area of the rollers. During or after a cleaning, particularly when the rollers have stopped completely, the suction effect is switched off completely so that it is possible to bring the yarn to be pieced into a piecing position along the wedge-shaped gap by pneumatic means in a simple way.
In other advantageous features of preferred embodiments of the invention, it is provided that, after the return of the yarn end, during the restarting, the effect of the suction device is first reduced, and is subsequently brought to the operational level. The reduced effect of the suction device produces a similar effect on the returned yarn end as the suction air current applied to the yarn worm, i.e., the yarn end to be pieced is neither pulled to deeply into the wedge-shaped gap and jammed nor is it transported out of the area of the wedge-shaped gap by the rollers. It is only subsequently, in the course of the actual piecing, that the operational suction effect is fully restored.
A preferred embodiment of an open-end friction spinning apparatus for carrying out the process is provided which has two friction surface parts that are equipped with a drive and form a yarn forming region. The apparatus includes at least one suction device that generates an air current aimed into the yarn forming region. A suction device control mechanism is provided for reducing the suction effect when spinning operations are interrupted and for interrupting the suction effect no later than a point when a yarn end is returned to the yarn forming region.
In other advantageous features of preferred embodiments of the invention, the suction control mechanism includes a reducing valve device and an interrupting valve device. In preferred embodiments of the invention, the reducing valve device and the interrupting valve device are disposed adjacent one another in an air flow direction between the suction device and a vacuum source.
In certain advantageous features of other preferred embodiments of the invention, the apparatus further includes a yarn guard control device that in the case of a yarn breakage, causes an interruption of the friction surfaces, a stopping of a feeding device which feeds fibers to the yarn forming region and controls the reducing valve device.
In certain advantageous features of other preferred embodiments of the invention, the interrupting valve device includes a given position when in an open position. The interrupting valve device includes an interrupting valve adjusting mechanism for adjusting the given position of the interrupting valve device.